FR2782685A1 - Brake servo mechanism for vehicle braking, has secondary push rod and secondary spring to reinforce amplification and provide two amplification ratios. - Google Patents

Abstract

The brake servo mechanism consists of a valve body (3), which slides within an outer case (2), with the valve stem (8) attached to the input shaft. A primary push rod (24) slides within the tubular part (8A) of the valve stem and is activated by the primary spring (25). A secondary push rod (26) is designed to slide around the periphery of the primary push rod, towards its forward extremity and a second spring (28), with a constant and larger pressure than the primary spring, acts between the second push rod and the valve stem.

Description

The present invention relates to a braking amplifier, and more

  particularly a braking amplifier which is constructed to allow a

  braking ratio be changed in two steps.

  A braking amplifier is known in the art, which comprises a valve body slidably disposed in a casing, a valve stem slidably arranged in the valve body and connected to the valve body.

  an input shaft to move with it, a first

  first rod pusher slidably arranged in

  a tubular part before the valve stem, a first

  first spring for pushing the first stem pusher forward with respect to the valve stem, and a disk

  reaction between a first end of an ar-

  outlet and one end face of the valve body

  to transmit a reaction that acts on the output shaft

  tie, through the first rod pusher and the first spring, to the valve stem and the input shaft (see for example the Japanese utility model publication

n 8337/1995).

  In the usual amplifier mentioned above, the braking amplifier being in the inactive state, the

  front end face of the first rod pusher

  substantially protruding forward of the front end face of the valve stem. When the brake amplifier is actuated, a reaction which acts on the output shaft causes the reaction disk to bulge, thereby causing it

  to abut against the front end face of the first

  first rod pusher. Subsequently, as the reaction increases to compress the first spring, the reaction disc abuts against the first rod pusher

  and the end face of the valve stem. As a result

  quence, an output is increased with an amplification ratio

  larger size provided that the reaction disk abuts against only the first rod pusher, and the output increases with an amplification ratio

  reduced provided that the reaction disk comes

  against both the first rod pusher and the valve stem. In this way, a customary arrangement allows an amplification ratio to be changed into two stages corresponding to a reduced driving area and a larger driving area of a brake pedal (input). We know in a brake amplifier that there is

  a hysteresis, which means a difference in

  when the brake pedal is depressed and where

  is released for an output of equal amplitude. In the

  usual finisher mentioned above, hysteresis over-

  comes not only in an amplification report area

  tion, but also in a report area of am-

  plication smaller or in an area where the sink

  applied to the brake pedal is larger.

  However, the presence of a hysteresis in an area where the depression of the brake pedal is greater results in, in fact, that the driver has the feeling

  that the ability to control braking is uncomfortable.

  As a result, when a brake amplifier is

  in which the amplification ratio can be modulated

  in two stages, it is desired that the brake amplifier has a hysteresis substantially equal to zero in an area where the depression of the brake pedal is greater. In view of the foregoing, the present invention

  provides a brake amplifier of the type indicated

  in which a second annular rod pusher is

  slidably arranged around the outer periphery

  the first rod pusher at its forward end, and a second spring having a greater resilience than the first spring is disposed between the second rod pusher and the valve stem, so that the brake amplifier is in the inactive state, the end face

  before the second rod pusher is positioned towards the

  of the front end face of the first rod pusher, so that when the brake booster is

  actuated, in a smaller driving area of the

  of the brake, the reaction disk is brought into abutment against the front end face of the first rod pusher to allow a reaction acting on the

  outlet is transmitted to the valve stem through

  of the first rod pusher and the first spring and in a larger depression area of the brake pedal, the reaction disk is abutted against the front end faces of the two rod pushers to allow a reaction that acts on the output shaft is transmitted to the valve stem via the

  two rod pushers and first and second spring.

  With this arrangement, when the braking amplifier

  swimming is actuated, a reaction that acts on the tree of

  the output causes the reaction disk to bulge

  by initially coming into abutment against the face of ex-

  tremité before the first rod pusher. The output increases

  with a larger amplification ratio under these conditions.

  Subsequently, when the depression applied to the

  the brake spring increases to cause a reaction increase, the first spring is compressed, after which the

  reaction disc also comes to an end against the se-

  rod push-rod, in addition to the first rod pusher.

  The output increases with a reduced amplification ratio to

from this point.

  In an area where the output increases with a reduced amplification ratio as mentioned above, or in an area where the depression applied to the brake pedal is

  bigger, when the brake pedal is released from the

  the reaction disk acts in such a way that a fluid circuit is switched by a valve mechanism which is mechanically connected to the valve stem,

  thus immediately causing a reduction in the output.

  However, since the second rod pusher and the valve stem are mechanically connected to each other through the second spring at this time, the inlet can not be reduced unless the reaction

  that has been bulged backward is brought forward.

  As a result, in an area where the output goes up with a

  ratio of amplification reduced, it follows that the hysteresis-

sis is practically nil.

  In this way, the ability to control braking

  can be improved in a driving area (or

  trea) greater than the brake pedal.

  The aims, characteristics and advantages of the pre-

  invention, as well as others,

  will appear better on reading the following description.

  of an embodiment thereof, made in reference

  the attached drawings, in which:

  FIG. 1 is a sectional view of a mode of

  use of the present invention, and

  FIG. 2 graphically represents the characteristic

  of the brake booster represented on the

  Figure 1 and a usual amplifier.

  Referring to the drawings, we will now describe

  an embodiment of the present invention. On the

  1, a braking amplifier 1 has an enve-

  2, in which a valve body substantially

  bulaire 3 is slidably arranged.

  A cupped power piston 4 is

  around the outer periphery of the valve body 3 and a diaphragm 5 made of rubber is applied

  on the back surface of the power piston 4. The di-

  5 separates the interior of the envelope 2 into a chamber

  with a constant pressure forward A and a chamber

  A valve mechanism 6, which is known per se, is disposed in the valve body 3 to switch a fluid circuit between the constant pressure chamber A

  and the variable pressure chamber B. The mechanism of

  pope 6 has a first annular valve seat 7

  formed on the valve body 3, a valve stem 8 is

  slidably in the valve body 3 to

  a location radially inward of the first

  first valve seat 7, a second valve seat

  11 formed on the rear end of the shank

  pope 8, and a shutter member 13 which is pushed back by

  a spring 12 from the right, as seen on the

  1, to bear on the two valve seats 7

and 11.

  A combination of the first valve seat 7 and

  an annular seat surface located on the element of ob-

  Fig. 13, which moves to or from contact with the first valve seat 7, defines a vacuum valve 14. A space positioned radially outwardly of the vacuum valve 14 communicates with the chamber. constant pressure A via a constant pressure axial passage 15 formed in the

  valve body 3. The constant pressure chamber A com-

  munic with an intake manifold through a pipe, not shown, mounted on the wall

  before the envelope 2 to introduce a negative pressure

tive.

  On the other hand, a combination of the second seat of

  pope 11 and an annular seat surface located on the closure member 13 which moves to or from the contact with the second valve seat defines an atmospheric valve 16. A space positioned so that intermediate or inward of the valve

  14 and to the outside of the air valve

  spherical 16 communicates with the variable pressure chamber

  B via a radial pressure passageway va-

  Riable 17 formed in the valve body 3.

  Finally, a space positioned radially towards the

  atmospheric valve 16 communicates with the

  mosphere through an atmospheric passage 18 defined by the inner periphery of the valve body 3

  and a filter 21 disposed therein.

  The valve stem 8 is slidably arranged

  in the inner periphery of the valve body 3, and has a rear end which is axially connected to a

  input shaft 22. The input shaft 22 is connected to a

  brake pad, not shown. A key member 23 extends radially in the valve stem 8 to engage therewith, so as to prevent extraction of the valve stem 8 from the inner periphery of the valve body 3 in a directed direction

rearward.

  In the present embodiment, a front portion of the valve stem and an arrangement associated therewith

  are improved to allow for changing the ratio of am-

  two-stage folding while reducing the hysteresis in a larger recess area of the pedal

  brake at a substantially zero value.

  Specifically, a front portion of the valve stem 8 includes a cylindrical stow 8A, in which is slidably arranged an axially rear portion of a first stem pusher 24 having the shape

of a circular rod.

  A front end of the stowage 8A is folded back

  inwardly to provide an abutment 8B, while the first stalk pusher 24 is provided with a protrusion

  annular 24A at its axial center.

  A first spring 25 which is loaded at a given load extends between the annular projection 24A and the bottom

  opposite of the stowage 8A. As a result, the first

  rod evening 24 is normally pushed forward by

  relative to the valve stem 8, and the brake amplifier

  1 being in the inactive state shown in FIG. 1, the first rod pusher 24 is held at its extreme forward position where the annular projection 24A is

  in abutment against the abutment 8B. At this moment, the end face

  back of the first rod pusher 24 and the bottom op-

  docked 8A are discarded. In this state, the

  outer periphery of the first rod pusher 24 which is disposed towards the front of the annular protrusion 24A made

  protruding forward of the stowage 8A.

  A second annular rod pusher 26 is slidably arranged around the outer periphery of the first rod pusher 24 toward its forward end. The trailing end of the second shank pusher 26 has an outer periphery which defines a radially outwardly extending rim 26A. A second spring 28 is disposed between the flange 26A and a ring 27 which is arranged

  around the outer periphery of the valve stem 8.

  The second spring 28 has a spring constant which

  is greater than the spring constant of the first res-

  fate 25 which is arranged in the stowage 8A, and is interpo-

  between the flange 26A and the ring 27 in its natural state

or non-compressed axially.

  In this state, the front end face 24B of the first

  first rod pusher 24 protrudes slightly through the second rod pusher 26, and therefore the front end face 24B of the first rod pusher 24 projects slightly forward of the front end face 26B of the second push rod 26. The amplitude of the projection is chosen to be smaller than the spacing

  existing between the rear end face of the first push

  evening of stem 24 and the opposite bottom of the stowage 8A, the am-

  brake 1 being in the idle state represented

shown in Figure 1.

  In this state too, a play is maintained between the rear end face of the second rod pusher 26 and

the abutment 8B of the stowage 8A.

  A stepped sleeve 31 having an inner periphery of reduced diameter extending towards its rear end is disposed in a surrounding manner with respect to the two rod pushers 24, 26 and the outer periphery of the stepped sleeve 31 is arranged at its rear end, in the inner periphery of the valve body

  3 while maintaining an airtight seal. The outer periphery

  the second push rod 26 extending in direction

  front end is slidably arranged

  from the back side, in the periphery of the

  upper of the stepped sleeve 31 extending towards its front end. It must be understood that the stepped sleeve

  31 substantially defines a portion of the valve body.

  An input shaft 32, which is known per se, is disposed in the constant pressure chamber A, and has a rear end in which a cavity 32A is formed.

  to be slidably arranged around the perimeter

  The cavity 32A of the output shaft 32 contains a reaction disk 33, which is interposed between the bottom of the cavity 32A and the face.

  front end of the stepped sleeve 31.

  The distal end (or front end) of the output shaft 32 protrudes outwardly extending through the forward axial portion of the casing 2 to be

  connected to a piston of a master cylinder, not shown.

  A return spring 34 is disposed between the wall

  before the casing 2 and the valve body 3 for

  Normally hold the power piston 4, the body of

  valve 3 and the like in their inactive position representing

ted.

  In the inactive state, the key member 23 is abutted against the inner wall surface of the casing 2 to prevent free movement to the

  right of the valve stem 8 with respect to the body of

  pope 3 so that a switching operation in the

  fluid circuit is carried out immediately by the mech-

  valve 7 each time the input shaft 22 and

  the valve stem 8 are actuated again.

  The braking amplifier 1 being in the inactive state

  tif, the front end faces 24B, 26B of the two push-

  rods 24, 26 are positioned slightly towards the rear of the front end face of the stepped sleeve 31,

  and are thus slightly spaced from the reaction disc 33.

  The front end face 24B of the first rod pusher

  24 protrudes slightly forward of the end face.

  before 26B of the second rod pusher 26. At this time,

  the second spring 28 is not compressed, but acts only

  as a spacer to maintain the second rod pusher 26 spaced from the front end (stop 8B) of the valve stem 8. Accordingly, the rim 26A of the second rod pusher 26 is positioned between the stop 8B of the valve stem 8 and the stepped end face of the sleeve

stage 31.

  The braking amplifier 1 being in the inactive state

  tif, the vacuum valve 14 is open while the atmospheric valve 16 is closed. As a result, a negative pressure is introduced into the constant pressure chamber A and the variable pressure chamber B.

  We will now describe the functioning of the

represented.

  In the arrangement described, when a brake pedal, not shown, is depressed, the brake amplifier 1 being in the inactive state as shown in FIG. 1, the input shaft 22 and the brake rod valve 8 are driven forward, thereby opening the atmospheric valve 16 while closing the vacuum valve 14. This introduces atmospheric air into the variable pressure chamber

  B, actuating the braking amplifier 1.

  A reaction from an outlet, acting on the output shaft 32, causes the reaction disk 33 to bulge rearwardly and abut against the front end face 24B of the first rod pusher 24. This

  corresponds to the point A represented on the graph of the

  gure 2, and is commonly called a "jump". The amplification ratio at the jump point can be described as (Sl + S2) / S2 where Sl represents the surface of the end face of the stepped sleeve 31 which abuts

  against the reaction disk 33, and S2 represents the sur-

  face of the front end face 24B of the first rod pusher 24. Thereafter, the output increases when such an amplification ratio increases to point B. Subsequently, when the depression (input) of the

  the brake pedal increases to bring an additional bulge

  rearward direction of the reaction disk 33, the first

  first spring 25 is compressed and the first rod pusher

  24 retracts backward relative to the stowage 8A.

  As a result, the front end face 24B of the first

  first rod pusher 24 is flush with the front end face 26B of the second rod pusher 26, and accordingly the

  reaction disk 33 abuts against the faces of

  before 24B, 26B of the two elements 24, 26.

  corresponds to the point B shown in FIG.

  After point B, the amplification ratio is

  compared to the previous amplification ratio.

  A mathematical expression of the amplification ratio

  then point B to a point of full load C can be given by (S1 + S2 + S3) / (S2 + S3) where S3 represents

  the surface of the front end face 26B of the second pbus-

  rod evening 26 which abuts against the reaction disc

  33, Sl is the surface of the front end face of

  stepped sleeve 31 which abuts the reaction disc

  33 and S2 is the surface of the end face 24B of

first rod pusher 24.

  Since S2 <(S2 + S3), it follows that the amplification ratio after point B is smaller than the amplification ratio that predominates in an area ranging from

  from point A to B. Consequently, the braking reaction

  that is transmitted to the driver will be detected as being small in an area from point A to point B, and will be detected as larger than before in an area following point B. After full load point C , the output increases with an amplification ratio consisting of the unit, and consequently, the braking reaction which is transmitted to a

  driver after the point of full load C, will be de-

  tected as being larger than it was before the point of full load C.

  In this way, in the present mode of

  the amplification ratio can be changed in two steps, from the actuation of the braking amplifier 1 to the point of full load C. Specifically, in a smaller depression area of the pedal As shown from point A to point B, located immediately after the actuation, a braking reaction of a small amplitude is transmitted to the driver, while a braking reaction more

  large will be transmitted to the driver in a zone of

  the braking pedal as

  from point B to point C, thus passing to the point of full load C o the reaction

braking is at maximum.

  As a result, it is possible to transmit a braking response that gives the driver a feeling of safety in an area where the output continues to increase

  while allowing a variation of the braking output

  from the actuation of the braking amplifier to the point of full charge is recognized

  as a gentle change by the driver.

  In an area where the amplification ratio is

  and the depression or entry of the brake pedal is greater, if the brake pedal is released in the enslaved state of equilibrium where the vacuum valve 14 and the atmospheric valve 16 are both closed the opening of the vacuum valve 14 results in

  immediate reduction of the output. However, as men-

  previously, in this state, the reaction disc 33 abuts against the front end faces 24B, 26B of the two pushers 24, 26, and the braking reaction is transmitted through the second spring 28 and the first spring 25, the valve stem 8 and the input shaft 22. As a result, there is no input change until the reaction disk 33 which has been bulged is brought back forward even if a reduction occurs immediately in the output as mentioned above.

  This means that in an area of magnification ratio

  reduced cation from point B to point C, the relationship between

  be the entry and exit remains virtually the same

  when the brake pedal is depressed and when it is

* bereaved, such a relationship being indicated by a

  tiline connecting points B and C. In other words, se-

  In this embodiment, the hysteresis which signifies

  An input difference for an equal output is practically zero in the area from point B to point C. In contrast to the embodiment described above, in a usual arrangement as mentioned above,

  in a reduced amplification report area as re-

  presented by a range from point B to point C, if the

  brake pedal is released in the state of equilibrium asser-

  vi, the output will be reduced as indicated by the lines

  interrupted. Thus, it can be seen that in the arrangement

  the hysteresis exists not only in a zone

  from point A to point B with a larger amplification ratio, but also in a zone from point B to

  point C having a reduced amplification ratio. As a result

  Therefore, with the construction of the prior art as mentioned, there is an uncomfortable braking control capability in a zone from point B

  at point C of greater depression.

  However, on the contrary, according to the present invention, the hysteresis can practically be canceled in a zone

  of greater depression from point B to point C,

  thereby improving the control capability of the braking

swimming.

  It should be noted that when the brake pedal is re-

  dropped into an area (from point A to point B) of

  reduced in intensity and with a higher amplification ratio, the output is reduced in accordance with a line

  rectilinear D similarly to the prior art

  pool. In other words, in the area from point A to point B, hysteresis occurs in the present mode of

  in a manner similar to the prior art

pool.

  Although the present invention has been described above in connection with a preferred embodiment thereof, it should be understood that many changes, many modifications and substitutions are possible.

  from the description above without leaving the

  took away from the scope of the present invention defined by

the appended claims.

Claims (2)

  1. Brake amplifier (1) having a body   valve (3) slidably disposed in a housing   veloppe (2), a valve stem (8) slidably arranged in the valve body and mechanically connected to an input shaft for movement therewith, a first rod pusher (24) arranged slidably in a front tubular portion (8A) of the valve stem, a first spring (25) for urging the first stem pusher forward with respect to the valve stem, and a   reaction disc (33) interposed between a first end   an output shaft (32) and an end face of the valve body for transmitting a reaction acting on the output shaft, via the first rod pusher and the first spring, to the stem valve and the input shaft, characterized in that it comprises a second annular rod pusher (26) slidably arranged around the outer periphery of the first rod pusher   (24) towards its front end, and a second res-   a fate (28) having a greater spring constant than the first spring (25) is disposed between the second rod pusher (26) and the valve stem (8), the front end face (26B) of the second pusher rod being disposed towards the rear of the end face   before (24B) of the first rod pusher, in the inactive state.   of the brake amplifier, the arrangement being such that when the brake booster is actuated, in a reduced depression zone of the brake pedal, the reaction disk (33) is brought into abutment against the face front end (24B) of the first rod pusher so that a reaction acting on the output shaft is transmitted, via the first rod pusher (24) and the first spring, to the rod of valve (8) while in a larger depression area of the brake pedal, the reaction disc is brought into abutment against the front end faces (24B, 26B) of the two rod pushers (24, 26). so that a reaction that acts on the output shaft is transmitted through the first   spring and the second spring, to the valve stem (8).   Braking amplifier according to Claim 1, characterized in that the tubular part (8A) of the valve stem (8) is provided at its front end with a stop (8B) which extends radially inwards. , the   first rod pusher (24) which is arranged in the   tubular portion of the valve stem being provided with a rim around its outer periphery at its center   axial axis, the first spring (25) being disposed between the   edge and bottom of the tubular part (SA),   the second stem pusher having a flange (26A) for   around its outer periphery at the level of its former   rear end, which extends radially outwards,   a ring (27) being mounted around the outer periphery   of the tubular part of the valve stem, the   wherein the spring (28) is disposed between the ring (27) and the rim (26A) of the second rod pusher, the arrangement being such that in the inactive state of the braking amplifier the rim (24A) of the first rod pusher (24) abuts the abutment (8B) on the valve stem from the rear side while the front end of the second spring (28), in its natural state, is positioned towards the before the stop   of the valve stem, so that the end face ar-   the second rod pusher (26) is removed from the   tee (8B) located on the valve stem (8).